EXHAUST SYSTEM FOR MOTORCYCLE WITH CATALYST INSIDE OF SILENCER

Abstract

 An exhaust system for a motorcycle includes an exhaust muffler (35F) with inclined side walls (47a, 47b) and is formed in an inverted trapezoid shape in a rear view. An exhaust gas conduit (51) passes through a front wall (47e) of the exhaust muffler (35F) and has a bent section (51 a) within the exhaust muffler (35F), which changes the flow direction of exhaust gas from longitudinal to lateral. A catalyst casing (50) which has one end connected to the exhaust gas conduit (51) is arranged to be inclined downwardly to one side.
The catalyst casing can thus be accommodated in the exhaust muffler arranged behind and beneath an engine main body, which makes it easy to ensure a bank angle and to ensure catalyst capacity and the flow length of exhaust gas to thereby improve a purification performance.

Description

[0001] The present invention relates to an exhaust system for a motorcycle in which exhaust gas discharged from a cylinder head of an engine main body mounted on a vehicle body frame is conducted into an exhaust muffler arranged in the rear of and below the engine main body, and a catalyzer casing of generally cylindrical shape retaining a catalyzer (catalyst) is accommodated in the exhaust muffler.

[0002] An exhaust system in which a catalyzer extending in the lateral direction of the vehicle is accommodated within an exhaust muffler is already known from Japanese Patent No. 4727503.

[0003] In the exhaust system disclosed in Japanese Patent No. 4727503, space within the exhaust muffler is used effectively, to thereby make it possible to increase a capacity of the catalyzer. However, since an exhaust gas conduit tube for introducing the exhaust gas into the exhaust muffler is connected to one lateral side of the exhaust muffler, the exhaust system as a whole increases in size in the lateral direction, which is disadvantageous as it then becomes difficult to ensure the maximum bank angle.

[0004] The present invention has been made in consideration of the above described circumstances, and it is an objective of at least the preferred embodiments to provide an exhaust system for a motorcycle which makes it easy to ensure a bank angle, and also ensures a capacity of a catalyzer and the flow length of the exhaust gas to thereby improve a purification performance.

[0005] According to a first aspect of the present invention, there is provided an exhaust system for a motorcycle in which exhaust gas discharged from a cylinder head of an engine main body mounted on a vehicle body frame is conducted into an exhaust muffler arranged in the rear of and below the engine main body, and a catalyzer casing of generally cylindrical shape retaining a catalyzer is accommodated in the exhaust muffler, comprising: the exhaust muffler being provided at opposite sides thereof in the lateral direction of the vehicle with a pair of lateral walls which are inclined so that their lower ends are closer to each other than their upper ends, and being formed in the shape of an inverted trapezoid in a longitudinal elevational view from the rear; an exhaust gas conduit passing through a front end wall of the exhaust muffler so as to conduct the exhaust gas; a bent section formed in an intermediate portion of the exhaust gas conduit within the exhaust muffler and changing the flow direction of the exhaust gas in the exhaust gas conduit from the longitudinal direction of the vehicle to the lateral direction of the vehicle; and a catalyzer casing having one end connected to a downstream end portion of the exhaust gas conduit within the exhaust muffler and being arranged in an inclined condition so as to become lower as it approaches one side in the lateral direction of the vehicle.

[0006] With this construction, in which the catalyzer casing slopes downwards to one side, it is possible to make it easy to ensure the bank angle, and the capacity of the catalyzer and the flow length of the exhaust gas can be ensured to thereby improve the purification performance.

[0007] Preferably, the exhaust system further comprises a tail pipe for discharging the exhaust gas from the exhaust muffler, wherein the tail pipe is joined to a rear upper part of the exhaust muffler on one lateral side, and the exhaust gas conduit is arranged on the other lateral side so as to pass through an upper part of the front end wall.

[0008] With this arrangement, the flow length of the exhaust gas can be increased within the exhaust muffler, so that adjustment can easily be carried out so as to improve output characteristics of the engine.

[0009] Preferably, the catalyzer casing has an elliptical transverse cross-sectional configuration, a longer axis of which extends in the longitudinal direction of the vehicle, and is formed flatter in the vertical direction.

[0010] Thus, even if the cross-sectional area of the catalyzer casing is increased so as to ensure the capacity of the catalyzer, it is still possible to ensure an appropriate distance between the bottom of the exhaust muffler and the ground while avoiding vertical enlargement of the exhaust muffler, which thereby contributes to ensuring the bank angle.

[0011] Preferably, the exhaust system further comprises a support means supporting the catalyzer casing and being fixed on the exhaust muffler, wherein the support means is configured to allow the exhaust gas to flow above and below the catalyzer casing.

[0012] With this arrangement, since the support means supporting the catalyzer casing is configured to allow the exhaust gas to flow on the upper and lower sides of the catalyzer casing, the external form of the exhaust muffler can be kept compact and the capacity of the exhaust muffler can be ensured.

[0013] Preferably, the exhaust muffler includes a first expansion chamber in which the catalyzer casing is accommodated and a second expansion chamber which is arranged to the rear of the first expansion chamber, laterally offset to one side and which is in communication with the first expansion chamber through a communicating tube, and a side stand which comes into contact with the ground in a standing position thereof is arranged on the other lateral side of the second expansion chamber such that, when the side stand is in the standing position, at least a portion of the side stand overlaps with the second expansion chamber in a side view.

[0014] With this arrangement, the exhaust muffler can be made compact in the longitudinal direction of the vehicle and the capacity of the exhaust muffler can be ensured.

[0015] In a preferred form, a rear end wall of the exhaust muffler forms a rear end of the second expansion chamber and is inclined forwardly and upwardly, and at least a rear part of the communicating tube is configured to be inclined rearwardly and downwardly.

[0016] Thus, the flow length of the exhaust gas can be made longer while extending the communicating tube to thereby increase flow speed of the exhaust gas.

[0017] In a further preferred form, the tail pipe for discharging the exhaust gas from the second expansion chamber is connected to a rear upper part of the exhaust muffler in such a way as to communicate with an upper part of the second expansion chamber.

[0018] With this arrangement, since the tail pipe which communicates with the upper part of the second expansion chamber is connected to the rear upper part of the exhaust muffler, the exhaust muffler can be made longitudinally compact, whereby concentration of mass can be achieved.

[0019] In a preferred form, within the second expansion chamber, a rear end of the communicating tube is arranged to the rear of a portion of the tail pipe which communicates with the second expansion chamber.

[0020] According to this arrangement, since the rear end of the communicating tube is located to the rear of the portion of the tail pipe which communicates into the second expansion chamber, the exhaust gas flowing out of the communicating tube within the second expansion chamber flows in such way as to turn around upwardly in a generally circular arc shape along the rear end wall, whereby the volume of the second expansion chamber can be used evenly and effectively.

[0021] A preferred embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:

FIG. 1 is a left side elevational view of a motorcycle;

FIG. 2 is a cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a view taken in the direction of arrow 3 of FIG. 2;

FIG. 4 is a view taken in the direction of arrow 4 of FIG. 2;

FIG. 5 is a longitudinal cross-sectional view of an exhaust muffler associated with the front bank when viewed from the right, the rear and above; and

FIG. 6 is a cross-sectional view taken along line 6-6 of FIG. 3.

[0022] An embodiment of the present invention will now be described with reference to accompanying FIGS. 1 through 6. In the following description, terms such as "front", "rear", "left", "right", "upper" and "lower" should be interpreted from the viewpoint of a rider riding on a motorcycle in normal use.

[0023] Referring first to FIG. 1, a vehicle body frame F of a two-wheeled motorcycle (as an example of a straddle type vehicle) includes a front fork 11 pivotally carrying a front wheel WF, a head pipe 12 supporting the front fork 11 in a steerable manner, a pair of left and right main frames 13 extending downwardly and rearwardly from the head pipe 12, a pair of left and right engine hangers 14 which are welded to the head pipe 12 and each of the main frames 13 and extend downwardly from the main frames 13, and a pair of left and right pivot frames 15 extending downwardly from each rear part of the main frames 13.

[0024] On the vehicle body frame F, there is carried an engine body 17 of a four cylinder V-type engine E, for example. In this embodiment, the engine body 17 pivotally supports a crankshaft 18 which extends in the lateral direction of the vehicle, and is supported by each lower portion of the pair of engine hangers 14, each intermediate portion of the main frames 13, and upper and lower portions of the pair of pivot frames 15. The engine main body 17 has a front cylinder bank BF and a rear cylinder bank BR, which are arranged in a V-shape in such a manner that the cylinders of each pair are arranged side-by-side in the axial direction of the crankshaft 18.

[0025] A front end portion of a swing arm 19 is pivotally supported in a swingable manner through a pivot shaft 20 on each vertically intermediate portion of the pair of pivot frames 15. At a rear end portion of the swing arm 19 is rotatably supported an axle 21 of a rear wheel WR.

[0026] The motive power from an output shaft 22 of a transmission accommodated within the engine main body 17 is transmitted through a chain drive means 23 to the rear wheel WR. The chain drive means 23 is composed of a drive sprocket 24 which is fixed to the output shaft 22, a driven sprocket 25 which is fixed to the axle 21 of the rear wheel WR, and an endless chain 26 which is wrapped around these sprockets 24 and 25.

[0027] A front part of the swing arm 19 is connected through a link mechanism 27 to each lower portion of the pair of pivot frames 15. A rear cushion unit (not shown) is provided between a component of the link mechanism 27 and the rear part of the main frame 13.

[0028] Above the rear bank BR of the engine main body, there is arranged a fuel tank 30 which is supported by the main frame 13. A rider's seat 31 arranged to the rear of the fuel tank 30 is supported by a rear part of the vehicle body frame F.

[0029] Front bank exhaust pipes 33F are connected to each cylinder of the cylinder head 32F of the front bank BF of the engine main body 17. The front bank exhaust pipes 33F pass under the engine main body 17 and extend rearwardly, and are joined in common to a front bank collecting exhaust pipe 34F. The front bank collecting exhaust pipe 34F is joined to a front bank exhaust muffler 35F which is located to the rear of and under the engine main body 17. Moreover, rear bank exhaust pipes 33R are connected to each cylinder of the cylinder head 32R of the rear bank BR of the engine main body 17 and extend rearwardly. The rear bank exhaust pipes 33R are connected to a rear bank collecting exhaust pipe 34R to the rear of the rider's seat 31. The rear bank collecting exhaust pipe 34R is joined to a rear bank exhaust muffler 35R which is located above the rear wheel WR.

[0030] The head pipe 12 of the vehicle body frame F is covered from the forward direction thereof with a front cowling 36. The front part of the vehicle body frame F and a part of the engine main body 17 are covered from each lateral side with a pair of left and right centre cowlings 37. The rear part of the vehicle body frame F, the rear bank exhaust pipes 33R, the rear bank collecting exhaust pipe 34R and the rear bank exhaust muffler 35R are covered with a rear cowling 38, which allows the rear part of the rear bank exhaust muffler 35R to project rearwardly therefrom. In addition, a portion of the front bank exhaust pipes 35F, the front bank collecting exhaust pipe 34F and the front bank exhaust muffler 35F are covered from beneath and from each lateral side with an under cowling 39, a front part of which is continuously connected to a lower part of the centre cowling 37.

[0031] Above the engine main body 17 and forwardly of the fuel tank 30 is arranged an air cleaner 42, which is common to the front bank BF and the rear bank BR. The air cleaner 42, a part of which is accommodated in a valley 43 between the front bank BF and the rear bank BR, is located between the pair of left and right main frames 13 and, together with the fuel tank 30, is covered with a cover 40.

[0032] Referring now to FIGS. 2 to 6, the front bank exhaust muffler 35F is constituted in accordance with a preferred embodiment of the present invention, and includes a first casing 47 forming a first expansion chamber 45, and a second casing 48 forming a second expansion chamber 46 which is smaller in volume than the first expansion chamber 45 and which is provided continuous with a rear part of the first casing 47.

[0033] The first casing 47 comprises a first right side wall 47a which is inclined in such a way that its lower end is located laterally further inward than its upper end, a first left side wall 47b which is inclined in such a way that its lower end is closer to the first right side wall 47a than its upper end, a first top wall 47c which connects upper end portions of the first right side wall 47a and the first left side wall 47b, a first bottom wall 47d which connects lower end portions of the first left side wall 47b and the first right side wall 47a, a front end wall 47e which connects front end portions of the first left side wall 47b, the first right side wall 47a, the first top wall 47c and the first bottom wall 47d, and a first rear end wall 47f which connects rear end portions of the first left side wall 47b, the first right side wall 47a, the first top wall 47c and the first bottom wall 47d.

[0034] The second casing 48 is provided continuous with a rear part of the first casing 47, such that the first rear end wall 47f of the first casing 47 functions as a front end wall of the second expansion chamber 46, and the second casing 48 is laterally offset to one side (the right side in this embodiment) to thereby be continuously connected to the rear part of the first casing 47. This second casing 48 comprises a second right side wall 48a which is inclined in such a way that its lower end is located laterally further inward than its upper end, located in a position where it substantially overlaps with the first right side wall 47a of the first casing 47 when viewed longitudinally from the rear, a second left side wall 48b located laterally inwardly of and facing the second right side lateral wall 48a and extending substantially vertically, a second top wall 48c which connects upper end portions of the second right side wall 48a and the second left side wall 48b and located such that a part thereof substantially overlaps with the first top wall 47c of the first casing 47 when viewed longitudinally from the rear, a second bottom wall 48d which connects between lower end portions of the second right side wall 48a and the second left side wall 48b and located such as to substantially overlap with the first bottom wall 47d of the first casing 47 when viewed longitudinally from the rear, the first rear end wall 47f connecting in common front end portions of the second right side wall 48a, the second left side wall 48b, the second top wall 48c and the second bottom wall 48d, and a second rear end wall 48e connecting in common rear end portions of the second right side wall 48a, the second left side wall 48b, the second ceiling wall 48c and the second bottom wall 48d.

[0035] When the entire front bank exhaust muffler 35F as constructed above is viewed longitudinally from the rear, it has first and second right side walls 47a, 48a which substantially overlap with each other on one side in the lateral direction of the vehicle, and the first left side wall 47b on the other side. The first and second right side walls 47a, 48a and the first left side wall 47b, which are located at opposite sides in the lateral direction of the vehicle, are inclined so that their lower ends are closer together than their upper ends, so that the front bank exhaust muffler 35F is formed in the shape of an inverted trapezoid in a longitudinal elevational view as seen from the rear of the vehicle.

[0036] Further, the rear end wall of the front bank exhaust muffler 35F, that is, the second rear end wall 48e of the second casing 48, is configured to be inclined forwardly and upwardly while forming the rear end of the second expansion chamber 46.

[0037] Within the front bank exhaust muffler 35F, there is accommodated a catalyzer casing (catalyst casing) 50 which retains a catalyzer (catalyst) 49 and is formed in a generally cylindrical shape. An end portion of the catalyzer casing 50 is connected to a downstream end portion of an exhaust gas conduit 51 which is in turn joined to the front bank collecting exhaust pipe 34F and passes through the front end wall 47e of the front bank exhaust muffler 35F, that is, the front end wall 47e of the first casing 47.

[0038] The exhaust gas conduit 51 passes through the front end wall 47e of the first casing 47 to thereby project into the first expansion chamber 45. In an intermediate part of this exhaust gas conduit 51 within the front bank exhaust muffler 35F, that is, in this embodiment, in an intermediate part in the first expansion chamber 45, there is formed a bent section 51 a for changing the flow direction of the exhaust gas within the exhaust gas conduit 51 from the longitudinal direction of the vehicle to the lateral direction of the vehicle.

[0039] Further, the catalyzer casing 50, one end of which is connected to a downstream end portion of the exhaust gas conduit 51 within the first expansion chamber 45 of the front bank exhaust muffler, is of generally elliptic transverse cross-sectional shape, with a longer axis extending in the longitudinal direction of the vehicle. The catalyzer casing 50, which is formed to be flatter in the vertical direction, is arranged in an inclined condition so that it becomes lower as it approaches one side in the lateral direction of the vehicle (the right side in this embodiment).

[0040] The catalyzer casing 50 is supported by a support means 52 which is fixed on the first casing 47 of the front bank exhaust muffler 35F. The support means 52 is configured to allow the exhaust gas to flow around the upper and lower sides of the catalyzer casing 50. In this embodiment, the support means 52 includes an upper support wall 53 which is fixed to an inner surface of the first top wall 47c of the first casing 47, and a lower support wall 54 which is fixed to an inner surface of the first bottom wall 47d of the first casing 47. The catalyzer casing 50 is supported between a lower part of the upper support wall 53 and an upper part of the lower support wall 54. An opening section 55 for allowing the exhaust gas to flow above the catalyzer casing 50 is provided in the upper support wall 53, while an opening section 56 for allowing the exhaust gas to flow below the catalyzer casing 50 is provided in the lower support wall 54.

[0041] A tail pipe 57 for discharging the exhaust gas from the front bank exhaust muffler 35F is joined to a rear upper part of the front bank exhaust muffler 35F on one lateral side (a right side in this embodiment). In this embodiment, an upstream end portion of the tail pipe 57 which communicates with an upper part of the second expansion chamber 46 is joined to a rear part of the second top wall 48c of the second casing 48. The tail pipe 57 is arranged so as to extend upwardly and rearwardly on the right side of the rear wheel WR. In addition, the tail pipe 57 is covered with a thermally insulating guard member 58 from the outside thereof. The thermally insulating guard member 58 is attached to the pivot frame 15 on the right side.

[0042] The exhaust gas conduit 51 is arranged so as to pass through an upper part of the front end wall 47e on the other lateral side (a left side in this embodiment) of the front bank exhaust muffler 35F.

[0043] A support member 59 is fixed to the lower portion of the pivot frame 15 on the left side, and a side stand 60 which is configured to come into contact with the ground in its standing position (as shown in FIGS. 3 and 6) is supported on the support member 59 so that it can rotate between the standing position and a retracted position (as shown in FIG. 1) raised upwardly from the standing position. When the side stand is in the retracted position, a coil spring 61 for energizing the rotation of the side stand 60 is disposed between the side stand 60 and the support member 59.

[0044] The side stand 60 is arranged on the other side (the left side in this embodiment) of the second expansion chamber 46 in such a manner that when the side stand 60 is in the standing position, at least a portion of the side stand 60 overlaps with the second expansion chamber 46 of the front bank exhaust muffler 35F in a side view, as shown clearly in FIG. 3.

[0045] The first expansion chamber 45 and the second expansion chamber 46 are connected with each other through a communicating tube 64 which passes through the first rear end wall 47f of the first casing 47. At least a rear portion (a rear half portion 64a in this embodiment) of the communicating tube 64 is formed so as to be inclined rearwardly and downwardly while facing the second rear end wall 48e, which as mentioned above is configured so as to be inclined forwardly and upwardly.

[0046] Further, within the second expansion chamber 46, a rear end 64b of the communicating tube 64 is arranged to the rear of the portion 65 of the tail pipe 57 which communicates with the second expansion chamber 46. That is, as shown in FIG. 3, the rear end 64b of the communicating tube 64 is arranged rearwardly of an imaginary vertical line L extending from a rear end of the portion 65 of the tail pipe 57 which communicates with the second expansion chamber 46.

[0047] The operation of this embodiment will now be described. The front bank exhaust muffler 35F has first and second right side walls 47a, 48a and first left side wall 47b which are located at opposite sides in the lateral direction of the vehicle so as to substantially overlap with each other when the whole thereof is viewed longitudinally from the rear. The first and second right side walls 47a, 48a and the left side wall 47b located at opposite lateral sides are inclined in such a way that their lower ends are closer to each other than their upper ends and are formed in the shape of an inverted trapezoid in an elevational view. The bent section 51 a for changing the flow direction of the exhaust gas from the longitudinal direction of the vehicle to the lateral direction of the vehicle is formed in the intermediate portion, within the exhaust muffler 35F, of the exhaust gas conduit 51 which passes through the front end wall 47e of the front bank exhaust muffler 35F so as to conduct the exhaust gas. Then, the catalyzer casing 50 which retains the catalyzer 49 and is formed in a generally cylindrical shape has one end portion connected to the downstream end portion of the exhaust gas conduit 51 within the front bank exhaust muffler 35F and is arranged in an inclined condition so as to be lower as it approaches one lateral side (the right side in this embodiment). With this construction, it is possible to make it easy to ensure the bank angle α of the motorcycle (as shown in FIG. 2), and the capacity of the catalyzer and the flow length of the exhaust gas can be ensured to thereby improve the purification performance.

[0048] Further, since the tail pipe 57 for discharging the exhaust gas from the front bank exhaust muffler 35F is joined to the rear upper part of the front bank exhaust muffler 35F on one lateral side (the right side in this embodiment), and the exhaust gas conduit 51 is arranged on the other lateral side (the left side in this embodiment) in such a way as to pass through the upper part of the front end wall 47e, the flow length of the exhaust gas is increased within the front bank exhaust muffler 35F, whereby adjustment can be easily carried out so as to make it possible to improve the output characteristics of the engine E.

[0049] The catalyzer casing 50 has a generally elliptical cross-sectional configuration, the longer axis of which extends in the longitudinal direction of the vehicle. Therefore, even if the cross-sectional area of the catalyzer casing 50 is increased in order to increase the capacity of the catalyzer 50, it is possible to ensure a distance between the bottom (that is, each of the first and second bottom walls 47d, 48d) of the front bank exhaust muffler 35F and the ground while avoiding vertical enlargement of the front bank exhaust muffler 35F, which can contribute to ensuring the bank angle α.

[0050] Further, since the support means 52 which supports the catalyzer casing 50 and is fixed on the front bank exhaust muffler 35F is configured to allow the exhaust gas to flow above and below the catalyzer casing 50, an external form of the front bank exhaust muffler 35F can be made compact and the capacity of the front bank exhaust muffler 35F can be ensured.

[0051] Moreover, the front bank exhaust muffler 35F includes the first expansion chamber 45 in which the catalyzer casing 50 is accommodated and the second expansion chamber 46 which is arranged to the rear of the first expansion chamber 45, offset to one side in the lateral direction of the vehicle, and which is in communication through the communicating tube 64 with the first expansion chamber 45. The side stand 60 which comes into contact with the ground in the standing position thereof is arranged on the other lateral side (the left side in this embodiment) of the second expansion chamber 46 in such a manner that, in its standing position, at least a portion of the side stand 60 overlaps with the second expansion chamber 46 in a side view. Therefore, the side stand 60 and the second expansion chamber 46 can be arranged side by side in the lateral direction of the vehicle, and the capacity of the front bank exhaust muffler 35F can be ensured, while compactly arranging the front bank exhaust muffler 35F in the longitudinal direction of the vehicle.

[0052] Further, the rear end wall of the front bank exhaust muffler 35F, that is, the second rear end wall 48e of the second casing 48, forms the rear end of the second expansion chamber 46 and is inclined forwardly and upwardly, and at least the rear part of the communicating tube 46 is configured to be inclined rearwardly and downwardly. Therefore, the flow length of the exhaust gas can be made longer while extending the communicating tube 64, to thereby increase flow speed of the exhaust gas.

[0053] Further, since the tail pipe 57 which discharges the exhaust gas from the second expansion chamber 46 is joined to the rear upper part of the front bank exhaust muffler 35F in a state of communicating with the upper part of the second expansion chamber 46, the front bank exhaust muffler 35F can be made longitudinally compact, whereby concentration of mass can be achieved.

[0054] In addition, since the rear end 64b of the communicating tube 64 is arranged, within the second expansion chamber 46, to the rear of the portion 65 of the tail pipe 57 which communicates with the second expansion chamber 46, the exhaust gas flowing out of the communicating tube 64 within the second expansion chamber 46 flows in such way as to turn around upwardly in a circular arc shape along the rear end wall 48e, whereby the volume of the second expansion chamber 46 can be used evenly and effectively.

[0055] While a preferred embodiment of the present invention has been described, the present invention is not limited to the above described embodiment, and various design changes and modifications may be made without departing from the scope of the present invention as defined in the appended claims.

Claims

1. An exhaust system for a motorcycle in which exhaust gas discharged from a cylinder head (32F) of an engine main body (17) mounted on a vehicle body frame (F) is conducted into an exhaust muffler (35F) arranged to the rear of and below the engine main body (17), and a catalyzer casing (50) of generally cylindrical shape retaining a catalyzer (49) is accommodated in the exhaust muffler (35F), comprising:

the exhaust muffler (35F) being provided at opposite sides thereof in the lateral direction of the vehicle with a pair of lateral walls (47a, 47b, 48a) which are inclined so that their lower ends are closer to each other than their upper ends, and being formed in the shape of an inverted trapezoid in a longitudinal elevational view from the rear,

an exhaust gas conduit (51) passing through a front end wall (47e) of the exhaust muffler (35F) so as to conduct the exhaust gas,

a bent section (51 a) formed in an intermediate portion of the exhaust gas conduit (51) within the exhaust muffler (35F) and changing the flow direction of the exhaust gas in the exhaust gas conduit (51) from the longitudinal direction of the vehicle to the lateral direction of the vehicle, and

a catalyzer casing (50) having one end connected to a downstream end portion of the exhaust gas conduit (51) within the exhaust muffler (35F) and being arranged in an inclined condition so as to become lower as it approaches one side in the lateral direction of the vehicle.

2. An exhaust system for a motorcycle according to claim 1, further comprising a tail pipe (57) for discharging the exhaust gas from the exhaust muffler (35F), wherein the tail pipe (57) is joined to a rear upper part of the exhaust muffler (35F) on one lateral side, and the exhaust gas conduit (51) is arranged on the other lateral side so as to pass through an upper part of the front end wall.

3. An exhaust system for a motorcycle according to claim 1 or 2, wherein the catalyzer casing (50) has a generally elliptical transverse cross-sectional configuration, a longer axis of which extends in the longitudinal direction of the vehicle, and is formed flatter in the vertical direction.

4. An exhaust system for a motorcycle according to any one of claims 1 to 3, further comprising a support means (52) supporting the catalyzer casing (50) and being fixed on the exhaust muffler (35F), wherein the support means (52) is configured to allow the exhaust gas to flow above and below the catalyzer casing (50).

5. An exhaust system for a motorcycle according to any one of claims 1 to 4, wherein the exhaust muffler (35F) includes a first expansion chamber (45) in which the catalyzer casing (50) is accommodated and a second expansion chamber (46) which is arranged to the rear of the first expansion chamber (45), laterally offset to one side and which is in communication with the first expansion chamber (45) through a communicating tube (64), and a side stand (60) which comes into contact with the ground in a standing position thereof is arranged on the other lateral side of the second expansion chamber (46) such that, when the side stand (60) is in the standing position, at least a portion of the side stand (60) overlaps with the second expansion chamber (46) in a side view.

6. An exhaust system for a motorcycle according to claim 5, wherein a rear end wall (48e) of the exhaust muffler (35F) forms a rear end of the second expansion chamber (46) and is inclined forwardly and upwardly, and at least a rear part of the communicating tube (64) is configured to be inclined rearwardly and downwardly.

7. An exhaust system for a motorcycle according to claim 5 or 6, wherein the tail pipe (57) for discharging the exhaust gas from the second expansion chamber (46) is connected to a rear upper part of the exhaust muffler (35F) in such a way as to communicate with an upper part of the second expansion chamber (46).

8. An exhaust system for a motorcycle according to claim 7, wherein, within the second expansion chamber (46), a rear end (64b) of the communicating tube (64) is arranged to the rear of a portion (65) of the tail pipe (57) which communicates with the second expansion chamber (46).

9. A motorcycle having an exhaust system as claimed in any preceding claim.

Drawing